1. Field of the Invention
The present invention relates to a method and a device for operating a fuel injection device of a motor vehicle, and a computer program that executes all steps of the method according to the present invention.
2. Description of the Related Art
A fuel injection device is known from published German Patent Application document DE 196 25 487 A1. In the case of that device, fuel is conveyed under high pressure into a high-pressure reservoir (in the case of a self-ignition internal combustion engine the so-called “common rail”) the pressure of which is controlled by a pressure regulator disposed in a control unit or by a corresponding pressure control valve and from which fuel is taken for injection via electrically controlled injection valves.
In operation of such an injection device, it may happen that owing to a malfunction the quantity (or mass) of fuel actually supplied to the high-pressure reservoir is not equal to the quantity envisaged for fuel injection and required for the pressure regulation. It is therefore known to carry out, at least occasionally, an examination of the fuel quantity balance in the high-pressure reservoir.
To prevent an inadequate fuel quantity balance, configuration of the injection device is effected with regard to the mentioned balance of incoming and outgoing quantities (masses) of fuel in the mentioned high-pressure reservoir, this being done in a manner known per se subject to estimated or empirically obtained properties of components of the injection device that determine the fuel flow, and in the worst case with a total failure of one or more of those components.
Alternatively or in addition, the mentioned configuration of the injection device is effected assuming a given standard fuel. Since the quality of the fuel, and in the present case especially the viscosity of the fuel, may be subject to fluctuations in various markets or regions, so that by way of example only a fuel having, for example, a relatively low viscosity is offered for sale, the configuration must also take those possible fluctuations into account.
In driving operation of a motor vehicle having such an internal combustion engine, the situation may therefore arise that properties or modes of behavior predicted for mentioned components are not maintained and, as a result, the mentioned balance of quantities of fuel flowing into and out of the mentioned high-pressure reservoir is no longer ensured.
In both of the mentioned cases of varying component properties and/or varying fuel quality or viscosity, the balance of the incoming and outgoing flows in the high-pressure reservoir would be disturbed in the mentioned situations and therefore the fuel pressure in the high-pressure reservoir would continuously or successively fall. As a countermeasure, the mentioned pressure regulator would increase the incoming flow into the high-pressure reservoir until a predefined control limit of the regulator, that is, the maximum possible incoming quantity in the case of the above-mentioned configuration, were reached. If the fuel pressure were then to fall further or if the fuel pressure were not to recover again from too low a level, the internal combustion engine would have to be shut down on the assumption that there was an external leak.